Apparatus and ejector for producing cold



March 25, 1969 J. A. RIETDIJK APPARATUS AND EJECTOR FOR PRODUCING COLD Sheet Filed June 26, 1967 FIG] NINVENTOR. JOHAN A. msruux AGE/V A. RIETDIJK 3,434,298

ND EJECTOR FOR PRODUCING COLD Sheet 2 of 2 F l G 2 I J A a I i m I a 2 m w n M V m M M n United States Patent US. Cl. 62115 Claims ABSTRACT OF THE DISCLOSURE A cold producing apparatus has a high pressure medium at a temperature below its inversion temperature, an ejector through which the medium 'is first expanded and collected in a container, and additional pressure-reducing means through which the medium is further expanded to a lower temperature and pressure, the ejector having the inside walls of its jet pipe portion heatable for volatizing contaminations from the medium deposited upon the walls.

In known apparatus for producing cold and/or for liquefying gases a supply of high-pressure medium is cooled in one or more heat exchangers to below the inversion temperature associated with that pressure of the medium. The medium is then throttled in one or more Joule-Kelvin cocks to a considerably lower pressure. With a correctly chosen pressure and temperature in the throttling process a temperature decrease of the medium or a phase transition of part of the medium, or both phenomena, will occur in the said Joule-Kelvin cock pins. The pressure reduced medium can then be brought in heat exchanging relationship with an object to be cooled or a medium to be cooled. If a phase transition has taken place, a part of the liquid formed may be conducted away from the apparatus, if desired. The lowpressure vapour formed is then conducted away to the atmosphere or returned to a compressor which supplies the high-pressure medium.

To obtain very low temperatures throttling must be carried out to very low pressures. If, for example, helium is used as the medium and cold is to be produced at a temperature of 42 K., throttling must be carried out to approximately 1 atm.; for 3.6" K. throttling is required to approximately 0.5 atm. For still lower temperatures throttling must be carried out to even lower pressures. This means that in a closed system the compressor will have to be very bulky while the low-pressure side of the heat exchangers will have to show a low resistance to flow. The result is that these known apparatus are complicated, bulky, and expensive. In addition, if it is an open system, i.e. the highpressure medium is derived from some source or other, while the pressure-reduced medium, after heat exchange with the object to be cooled, is conducted away to the atmosphere, when cold has to be supplied at temperatures with which a subatmospheric pressure is associated, the apparatus cannot blow off automatically. So measures will have to be taken to conduct away the pressure-reduced medium from the apparatus.

A further drawback of the said apparatus is that in the Joule-Kelvin cocks the pressure energy of the high-pressure medium is uselessly dissipated which consequently means a loss.

The invention relates to an apparatus for producing cold and/ or for liquefying gases in which the drawbacks of the above described apparatus are mitigated. This apparatus comprises at least one supply for medium under high pressure, which supply communicates with one or ice more heat exchangers in which the high-pressure medium is cooled to below the inversion temperature associated with that pressure, the apparatus comprising at least one ejection being a jet pipe to which at least part of the cooled high-pressure medium can be supplied, the outlet of said ejector communicating, if required through a first container for receiving the pressure-reduced medium, on the one side through one or more of the said heat exchangers, with an outlet through which the pressurereduced medium can leave the apparatus and, on the other side, through one or more throttle devices and, if required, a heat exchanger, communicates with one or more further containers in which lower pressures prevail and which each communicate with the suction side of the said ejector.

An ejector is to be understood to mean within the scope of the present invention an apparatus in which the potential energy of a high-pressure (primary) medium is wholly or partly converted into kinetic energy, said kinetic energy being used, at least partly, for raising the pressure of a second (secondary) medium.

In the apparatus to which the invention relates the energy of the high-pressure medium supplied to the ejector is at least partly used for sucking off the vapour from the low-pressure container and bringing .it to the pressure prevailing in the duct system through which the pressurereduced medium is conducted away from the apparatus. The cold can then be supplied at a pressure which is lower than the outlet pressure. This has the advantage that in an open system the apparatus can blow ofl? automatically while the cold is supplied at a pressure lower than the blowing-off pressure. In a closed system in which a compressor is provided which communicates with its outlet with the supply of high-pressure medium and communicates, with its inlet, with the outlet for pressure-reduced medium, the pressure ratio of the compressor will be considerably lower than is the case in the apparatus in which the high-pressure medium is reduced in pressure in Joule- Kelvin cocks.

In the apparatus to which the invention relates the pressure energy of the medium supplied to the ejector is no longer uselessly dissipated but is used for pumping up the vapour from the low-pressure container to the suction pressure of the compressor. In this manner an apparatus is obtained having a higher efficiency and a much more favourable pressure ratio in the heat exchanger and the compressor than is the case in apparatus in which Joule- Kelvin cocks are used.

The apparatus to which the present invention relates may be used in particular it cold has to be supplied at very low temperatures. Of late one has been very interested in cold supplied at temperatures which lie below 4 K., in particular for cooling super conductive coils, arithmetic and memory elements, respectively, of electronic computers, and so on. As already said, these low temperatures are associated with very low vapour pressures above the liquid bath in the 1ower-pressure container in which the object to be cooled is placed. If, for example, cold is to be supplied at 1 Kelvin, a vapour pressure in the lowpressure container of 0.12 mm. Hg. is associated therewith. In order to be able to maintain these low-pressures in the further container, a very good suction operation of the ejector is required.

At these low temperatures the danger exists that contaminations in the medium deposit in the solid state on the walls of the jet pipe of the ejector. At these low temperatures helium will usually be used as the medium, contamina-tions, if any, in said helium, for example, hydrogen, depositing in the solid state on the wall of the jet pipe. As a result of this deposition the operation of the ejector decreases which has an increase of the pressure in the low-pressure container for its result. In order to ensure a good operation of the ejector, and, particularly, a minimum attainable suction pressure, the walls of the jet-pipe must be liberated from contamiuations deposited on them as soon as the pressure in the lower-pressure container exceeds a given value. This could be done by means of mechanical scraping means which are moved along the wall of the jet pipe of the ejector. It will be clear that at the prevailing very low temperatures this will entail an extremely complicated construction in which it cannot be avoided that insulation losses occur as a result of which heat will flow to the ejector.

In order to avoid the above drawback in a simple manner the apparatus according to the invention is characterized in that a firing device, preferably an electric firing device, is arranged near each of the ejectors in and/or around the wall of the jet pipe for the high-pressure medium. The said firing device enables the wall of the jet pipe of the ejector to be brought for a moment at a somwha-t higher temperature as a result of which the contaminations deposited on the wall will volatilize after which the ejector will again show its normal operation.

A further favourable embodiment of the apparatus according to the invention is characterized in that it comprises a control device which switches on the firing device for a short period of time if the pressure and/ or the temperature in the further containers exceed a given value, which value may be adjustable.

According to a further embodiment of the apparatus it is also possible to cause the control device to switch on the firing device if the pressure in the supply for highpressure medium to the ejector exceeds a given value, which value may be adjustable.

Since it is of importance that the deposited contaminations are removed with a minimum of supply of heat, a favourable embodiment of the apparatus according to the invention is characterized in that the part of the wall of the jet pipe which is in a heat conducting contact with the firing device or which forms part of the firing device is constructed so that it has a low thermal capacity and is in a poor heat conducting contact with the remaining part of the jet pipe. With this embodiment it will be possible to bring the relative part of the wall at a somewhat higher temperature with a very small amount of heat.

The invention further relates to an ejector suitable for use in an apparatus according to the invention. This ejector comprises a jet pipe for the high-pressure medium, a diffuser for conducting the expanded medium, and a suction aperture for a medium to be sucked. This ejector is characterized in that in and/or around the wall of the jet pipe in a firing device is provided, preferably an electric firing device. This ejector may furthermore comprise the further structural features already described above.

In order that the invention may readily be carried into effect it will now be described in greater detail, by way of example, with reference to the accompanying drawing, in "which FIG. 1 diagrammatically shows an apparatus for producing cold and/ or for liquefying gases in which apparatus an ejector is provided. FIGS. 2 and 3 show on an enlarged scale two embodiments of ejectors as provided in the device shown in FIG. 1.

Referring now to FIG. 1, reference numeral 1 denotes a compressor. The compressed medium is first conducted to a cooler 2 where the heat of compression is conducted away. The compressed medium then flows through the heat exchanger 3 where it exchanges heat with lowerpressure medium. The high-pressure medium is then cooled in heat exchanger 4 by means of a cooling device 5 to a temperature of, for example, 60 K. The high-pressure medium then flows through the heat exchanger 6 where it exchanges heat again with lower-pressure medium. The high-pressure medium is then cooled in heat exchanger 7 by means of a cooling device 8 to a temperature of, for example, 15 K., after which it exchanges heat in heat exchanger 9 with expanded medium. The highpressure medium then has a temperature which lies below the inversion temperature of that medium at the pressure prevailing. The medium then enters an ejector 10 in which it is reduced in pressure. The ejector communicates with an outlet 11 comprising a container 12. The vapour space of the container 12 communicates through heat exchangers 9, 6 and 3 with the inlet side of the compressor 1. Condensate from the container 12 can flow, through a heat exchanger 13 and throttle valve 14 in which the liquid is further reduced in pressure, to a container 15 in which a lower pressure prevails than in the container 12.

The vapour space of the container 15 communicates through heat exchanger 13 with the suction side 16 of the ejector 10. In the container 15 a cooling spiral 17 is arranged through which a medium to be cooled can flow. Instead of the cooling spiral 17 an object to be cooled, for example, a super-conducting coil or a cryogenic arithmetic or memory element of an electronic computer may be arranged in the container 15. In this apparatus helium is present as a medium. The compressor 1 compresses helium to a pressure P1. This high-pressure medium is cooled in heat exchangers 2, 3, 4, 6, 7 and 9 to below the inversion temperature of said medium at this pressure. The high pressure medium is then applied to the ejector 10. In this ejector the medium experiences a reduction in pressure at which the potential energy is partly converted into kinetic energy, said kinetic energy being again partly used for bringing the low-pressure medium at pressure. The medium which leaves the ejector with a pressure P2 is received in a container 12. The vapour with a pressure P2 may then flow back again to the compressor through the said heat exchangers. The said liquid is throttled in the throttle device 12 to a pressure P3 which is associated with the temperature at which the cold must be supplied. The vapour in the container 15 of pressure P3 is sucked off by the ejector 10 and brought at the pressure P2 of the container 12. Before entering the ejector 10 the vapour from the container 15 exchanges heat with medium of higher pressure in the heat exchangers 13 and 18. So in this device the compressor operates between the pres sures P2 and P1 so that this compressor structurally is much simpler than in the device in which throttling is effected in Joule-Kelvin cocks and in which the compressor operates between the pressures P3 and P1. FIG. 1 shows, by way of example, one embodiment of a cold-producing device in which an ejector is used. Further embodiments of similar devices are described in British patent application 53,418/65.

FIG. 2 shows the ejector 10 on an enlarged scale. The high-pressure medium is supplied at the area 20 to the part 21 of the jet pipe of the ejector. In the wall of the part 21 of the jet pipe a firing device 22 is arranged. This firing device is shown in the figure as an electric firing device but it will be clear that, if required, other firing devices may also be used. For example, a heat-conducting connection between the wall of the part 21 of the jet pipe and the atmosphere may be effected as a result of which a quantity of heat can be conducted from the atmosphere to the jet pipe at the desired instant. The diffuser part of the ejector is denoted by reference numeral 24 while the suction aperture for a medium to "be sucked is denoted by reference numeral 25. The high-pressure medium which enters the jet pipe at the area 20 will have a higher temperature than the medium which leaves the jet pipe at the area 26. It is possible that at the prevailing low temperatures contaminations of hydrogen in the supply of helium are deposited in the solid state on the wall of the jet pipe 21. As a result of this the passage is narrowed so that the operation of the ejector is interfered with and a lower suction pressure is obtained. When the pressure in the container 15 increases as a result and exceeds a. given value, the control device which is diagrammatically denoted by reference numeral 27 will receive a signal to that effect via indicator 27 and will switch on the firing device for a short period of time. During this short period of time a quantity of heat is applied to the surface of the jet pipe as a result of which the temperature thereof increases somewhat and contaminations deposited thereon evaporate after which the ejector again shows its normal operation. Instead of controlling the pressure in the container 15 it is also possible to control the temperature in the container since this is directly dependent upon the pressure prevailing in the container. Alternatively, the control device may control the pressure which is measured in the duct for the high-pressure medium before the medium enters the ejector. If this pressure reaches too high values, the firing device may again be switched on for a short period of time. Although, as shown in FIG. 2, the wall of the jet pipe may consist of a normal heatconducting material, it will be clear that it has advantages to remove the deposited contaminations with a minimum of heat supply. For that purpose, the part 28 of the wall of the jet pipe in FIG. 3 where deposition of contaminations can take place is manufactured from heat-conducting material. This part of the wall is constructed so that it has a small mass and a low thermal capacity so that a rise in temperature can already be obtained with very small supply of heat as a result of which the contaminations will volatilize. The remaining part of the wall of the jet pipe is manufactured from a heat-insulating material, for example, a synthetic material or glass. As a result of this the thermal conductivity through and the storage of heat in the wall of the jet pipe 21 is substantially excluded.

As may be clear from the above, deposits, if any, on

the walls of the jet pipe of the ejector in the apparatus.

according to the invention can very easily be removed without this requiring additional complicated movable structural components.

What is claimed is:

1. A cold producing apparatus comprising a medium supply under high pressure and at a temperature below the inversion temperature associated with said pressure, at least one ejector having a jet pipe portion to which at least part of said high pressure medium can be supplied the jet pipe having interior walls on which contaminations of the medium may become deposited, at least one container with which the outlet of said ejector communicates, at least one pressure reducing device, medium from said container being further reduced in pressure through said pressure reducing device, and a heating device mounted in operative relation with the wall of said jet pipe, for volatizing the contaminations deposited on said wall, said ejector having an additional suction inlet, and said apparatus further comprising a second lower pressure container having an inlet for receiving said reduced pressure medium from said device and having an outlet for conducting gaseous medium therein to said suction inlet of the ejector.

2. A cold producing apparatus as defined in claim 1 further comprising a control device for switching on said heating device for a relatively short period of time when the pressure and/or temperature of said pressure reduced medium exceeds a given value in said container.

3. A cold producing apparatus as defined in claim 1 further comprising a control device which switches on said heating device for a short period of time when the pressure in the supply for said high pressure medium to the ejector exceeds a given value.

4. A cold producing apparatus as defined in claim 1 wherein part of the wall of said jet pipe is in heatconducting contact with said heating device, has a low thermal capacity, and is in poor heat-conducting relationship with the remaining part of the wall of said jet pipe.

5. For use in a cold producing apparatus having a high pressure medium supply and at least one heat exchanger for cooling the medium, an ejector which comprises a jet pipe portion for receiving said high pressure medium, a diffuser for conducting away the expanded medium, a suction aperture upon which a vacuum can be drawn, and means for heating the wall of said jet pipe for volatizing contaminations of the medium deposited on the wall.

6. An ejector as defined in claim 5 wherein a part of the wall of said jet pipe which is in heat-conducting contact with the heating means has a low thermal capacity and is in poor heat-conducting relationship with the remaining part of the wall of said. jet pipe.

7. A cold producing apparatus comprising a medium supply under high pressure, at least one heat exchanger for cooling said medium to a temperature below the inversion temperature associated with said pressure, at least one ejector to which at least part of the cooled high pressure medium can be supplied for expansion therein, the ejector having a jet pipe portion including an inlet and an outlet, a container for receivig medium from said ejector outlet, the container having a first outlet through which said reduced pressure medium is dischargeable and a second outlet, at least one throttle device for receiving said reduced pressure medium from said second outlet and further expanding the medium, and a heating device operative with the wall of said jet pipe for volatizing contaminations in said medium supply deposited on said wall.

8. In a method for producing cold having the steps of (a) compressing a medium to a high pressure, (b) cooling the medium to a temperature below the inversion temperature corresponding to that pressure (c) flowing the cooled medium to the jet pipe portion of an ejector, and (d) expanding the medium through the ejector to a state of reduced pressure and temperature with a resulting deposit of contaminations from said medium on the inner walls of said jet pipe, and (e) conducting at least some of said reduced pressure medium to a suction inlet of said ejector, the improvement in combination therewith comprising heating said inner walls and thereby volatizing and eliminating said contaminations.

9. A method as defined in claim 8 wherein said heating comprises connecting electric heating means to said jet pipe and applying electric power thereto.

10. A method as defined in claim 9 wherein heating further comprises insulating said heating means and the heated portion of the ejector from the remainder of the ejector.

References Cited UNITED STATES PATENTS 2,146,797 2/1939 Dasher 62-500 3,277,660 10/1966 Kemper 62-500 3,360,955 l/l968 Witter 62-514 WILLIAM J. WYE, Primary Examiner.

U.S. Cl. X.R. 

